Energy storage flywheels accumulate and store energy in the form of kinetic energy of a spinning inertia. In other words, an energy storage flywheel stores kinetic energy by essentially continually spinning. When desired, the kinetic energy stored in the flywheel may be accessed and released by transferring the kinetic energy. For example, the energy stored in a typical flywheel may be released as electrical power by engaging a shaft coupled to the flywheel with a generator. Typical energy storage flywheel systems consist of a large inertia wheel coupled to a motor-generator via a shaft. During certain periods, the motor typically converts input energy into stored kinetic energy (e.g., via rotation of the large inertia wheel), and the generator converts the stored kinetic energy into electrical energy. For example, taking into consideration a power plant and a power distribution grid, during periods of lower electricity use (e.g., nighttime), electrical energy may be stored in the flywheel, whereas during periods of higher electricity use (e.g., daytime), the electrical energy may be extracted from the flywheel and directed back into the electrical grid.
Energy storage flywheels have several typical applications. One typical application for energy storage flywheels is regenerative braking. This may include regenerative braking of trains, vehicles, and wind turbines, and braking drill strings as they are lowered into an oil or gas well. Another typical application for energy storage flywheels is providing peak power-assist for vehicles, machinery, and other processes. For example, this technique may be used for the purposes of lowering surcharges from power utilities for peak power demand, obtaining more efficient machinery by designing for efficiency without the constraint of meeting peak power demand, eliminating some machines from a cluster if they only function as peak power sources, and allowing the remaining machines to operate at higher loading, which typically yields higher efficiencies. Yet another typical application for energy storage flywheels includes acting as mechanical batteries for storing energy until the energy/power is required for local usage, or until power curtailment is lifted and the stored flywheel energy is delivered to the grid.
As described in greater detail below, traditional energy storage flywheels are attached to or integrated with long shafts, separate motor-generators coupled to the shafts, and separate bearing assemblies coupled to the shafts. As such, it is now recognized that conventional energy storage flywheel systems can occupy a large amount of space and be extremely expensive to manufacture. Further, it is now recognized that techniques for making energy storage flywheel systems more compact, more efficient, and less expensive are desired.